Numerous coatings have been used by skilled artisans for years as colorants and opacifiants for architectural, appliance, and automotive glass. Such coatings usually involve ceramic frit compositions that are composed of a mixture of metal oxides in an organic-based medium. The organic-based medium often includes materials such as pine oils, mineral oils, and other petroleum-based products. Such organic based coatings, however, give rise to numerous environmental and commercial concerns. Additionally, the metal oxide used in many such organic based compositions is lead oxide. Lead requires special care and handling during coating processes and in disposal, and is currently prohibited in paint formulations by United States Environmental Protection Agency regulations. Other metal oxides, such as cadmium and chromium, can also be added as pigments in such organic-based coatings, but are also considered hazardous. It is desirable to provide a water-based coating to take the place of such organic based and toxic material containing coatings.
Inorganic coating composition containing no lead and including water based alkali metal silicate solutions, pigments, and other components are known, for example, the coating compositions disclosed by U.S. Pat. No. 5,518,535 to Boaz and U.S. Pat. No. 5,510,188 to Vockler. However, it is often a problem to maintain control of the viscosity of such known coating solutions. The lack of control of the viscosity can lead to either viscosity build-up or running or blurring of the coating material. It is also a problem in such coatings to maintain consistent viscosity properties within a coating mixture.
Additionally, such known coating formulations often have difficulty with lack of stability and homogeneity. Often the materials suspended in the formulation will separate out in a short period of time such that the formulations are not homogeneous, and have re-crystallization problems. Each of these problems results in the coating formulations being difficult to use and having a shortened shelf life.
It is desirable to provide a water-based inorganic coating formulation that also provides for better control of the viscosity, the homogeneity, the re-crystallization, the stability, and the material separation properties of the formulation.